1. Field of the Invention
This present invention relates to substrate processing and, in particular, to methods and apparatus for detecting the presence or position of a substrate located within a substrate processing system.
2. Description of the Related Art
Semiconductor devices, such as transistors, diodes, and integrated circuits, are typically fabricated on a thin slice of semiconductor material, termed a substrate or wafer. The substrate is fabricated within a substrate processing system, which typically includes one or more load locks, a wafer handling module and one or more processing modules. The one or more load locks provide a substantially particle free environment from which substrates may be selectively withdrawn into the substrate handling module. The substrate handling module typically includes a substrate handler, which is configured to move substrates to/from the one or more load locks and to/from the one or more processing modules.
There are several general problems that are associated with prior art substrate processing stations. For example, as the substrate is moved within the processing station, the substrate can become misaligned or mispositioned for various reasons. Such mispositioning can result in damage to the substrate as it is moved within the processing station and/or errors in the fabrication process if the mispositioning occurs within a processing module. As such, some substrate processing system include several sensors to monitor the position of the substrate position. Each sensor adds to the complexity and cost of the processing system. These sensors are also typically difficult to maintain and require frequent alignment.